Disclosed herein is a phase separation ink comprising at least one crystallizable component comprising a material that crystallizes as it cools from a first ink jetting temperature to a second temperature that is lower than the ink jetting temperature, wherein the second temperature is sufficient to initiate crystallization of the at least one crystallizable component; at least one amorphous component comprising a material that remains amorphous at the second temperature; an optional colorant; wherein the at least one crystallizable component and the at least one amorphous component are in a molten, single phase state at the first ink jetting temperature; wherein at the second temperature, the phase separation ink comprises a crystalline phase comprising the at least one crystallizable component and an amorphous phase comprising the at least one amorphous component; wherein the amorphous phase of the at least one phase separation ink substantially penetrates into the final image receiving substrate; and wherein the crystalline phase of the at least one phase separation ink substantially remains on the surface of the final image receiving substrate.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, which is hereby incorporated by reference herein in its entirety, ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
There are at least three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing wherein an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface such as at the liquid/air interface of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
In a typical design of a piezoelectric ink jet device utilizing phase change or solid inks printing directly on a substrate or on an intermediate transfer member, such as the one described in U.S. Pat. No. 5,372,852, which is hereby incorporated by reference herein in its entirety, the image is applied by jetting appropriately colored inks during four to eighteen rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the print head with respect to the substrate in between each rotation. This approach simplifies the print head design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Thermal ink jet processes are well known and are described, for example, in U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224 and 4,532,530, the disclosures of each of which are hereby totally incorporated herein.
As noted, ink jet printing processes may employ inks that are solid at room temperature and liquid at elevated temperatures. Such inks may be referred to as hot melt inks or phase change inks. For example, U.S. Pat. No. 4,490,731, which is hereby incorporated by reference herein in its entirety, discloses an apparatus for dispensing solid ink for printing on a substrate such as paper. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by the heater in the printing apparatus and utilized (i.e., jetted) as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the colorant to substantially remain on the surface of the substrate instead of being carried into the substrate (for example, paper) by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a phase change ink in ink jet printing are thus elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
Solid inks for piezoelectric ink jet printing have been designed to successfully print in a transfix mode wherein the ink is jetted onto an intermediate transfer drum. In the transfix printing process, the ink cools from the jetting temperature (broadly, from about 75° C. and to no higher than about 180° C., and typically from about 110° C. to about 140° C.) to the drum temperature (typically from about 50° C. to about 60° C.), and, subsequently, as a substantially solid phase, the ink is pressed into a paper substrate. Such a process provides a number of advantages including vivid images, economy of jet use, and substrate latitude among porous papers. However, such ink designs can present problems when applied to coated papers. In general, the ink and the print process can fail to provide sufficient image durability in response to paper handling stresses such as scratch, fold and rub stresses. Moreover, key elements of the ink design that provide good transfix behavior may not be required or desired in a direct to paper architecture.
Currently available phase change or solid ink printing processes are suitable for their intended purposes. However, a need remains for a printing process and phase change ink providing improved properties including improved adherence of image to paper, improved image permanence, improved robustness against mechanical stresses, and improved image characteristics including surface gloss level. Further, a need remains for a direct to paper printing process for phase separation inks.
The appropriate components and process aspects of the each of the foregoing U.S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.